The present invention is generally related to computer networking,
A high availability network switch has redundant management modules which are generally responsible for processing various exceptional network stimuli, e.g., exceptional protocol packets that are difficult or economically unjustified to perform in hardware, learning new network device addresses, and port status changes. All other switching and routing functions are generally performed autonomously in hardware. It is possible to briefly interrupt the management module's processing of exceptional network stimuli, as long as the interruption does not violate minimum network response times, e.g., the shortest protocol timeout window.
During operation, the switch must continuously send updated state information from the active management module to the standby management module. This is necessary so that if a failure of the active management module occurs, the standby management module has the same state and can seamlessly take over. In a highly dynamic network, switch state is rapidly changing.
Messages used to transport state between the management modules are subject to latency for various reasons, e.g., operating system task context switch time and management module to management module link speed. At any instant, a comparison of the simultaneous measurement of state within the redundant management modules would show they are out of synchronization due to latency induced time lags. The management modules will only appear to be in synchronization when both are quiescent.
During development of software for a switch, the designers have a need to test for equivalent state between the active and standby management modules to determine whether they have correctly coded the redundant aspects of their designs.